1. Field of Invention
The invention relates to a stratified bulk material filter, in which a housing receives several vertical filter layers of bulk material which are transversely traversable by gas flow, are enflanked at both sides by limitations may be charged with bulk material from above and from which bulk material is extracted, the one side of each of the layers delimiting a flow arrival space of a crude gas and the oppositely situated side delimiting a flow departure side for purified gas.
In the case of stratified bulk material filters of this kind, the bulk material consists of granular material, e.g. fine gravel, for deposition of particles from the crude gas and/or for example granules or granular calcium carbonate for dry adsorption of noxious gases contained in the crude gas, and/or of granules for instigation of a catalytic action on chemical reactions.
2. Description of the Prior Art
The bulk material in vertical layers of bulk material traversed transversely by gas flow is primarily charged by deposited particles at the flow arrival side, in almost all practical applications. It is advantageous for this reason that the bulk material be freed of particles selectively at the flow arrival side, or rather that greatly contaminated grains or such as are exhausted by adsorption are removed from the layer of bulk material and are replaced by uncontaminated particles which slip into position. To secure removal and/or exchange of particles, it has already been proposed in DE-OS No. 32 46 183 that the delimitation of the bulk material layers should be so constructed at the flow arrival side that slopes of the bulk material may form, for example on horizontal surfaces or horizontal branches of angular delimiting sections. By imposing oscillations or tipping displacements on the horizontal sections of the delimitations, adhering dust and bulk material particles of the slopes may be caused to drop down sideways to be extracted, and replaced by after-sliding bulk material particles, to secure the adequate adsorption of noxious gases or to keep the throughflow resistance as low as possible throughout the service period of the filter. The known aforesaid embodiment comprises a complex, heavy and costly structure in practice and has not gained acceptance for this reason.
It is also known from DE-B No. 12 41 243 and DE-B No. 16 57 125 that bulk material of bulk material layers on which particles adhere during the throughflow of crude gas may be freed from adhering particles by a counterflow flushing operation. To this end, the bulk material was installed in bulk material layer filters within horizontal boxes or containers having a permeable bottom and a permeable or open top and the bulk material was then traversed for cleaning purposes by a pure gas in counterflow to the crude gas, to free and remove the particles deposited on the bulk material from the crude gas. Whilst doing so, the bulk material always remains the same in the containers. It has been frequently observed that in operation of this structure of the bulk material layers an unequal throughflow of the crude gas occurred since the cleansing of the bulk material could not be performed with sufficient uniformity across the flow impingement surface and the crude gas then preferentially flowed through the bulk material areas which had been most extensively cleansed and consequently had the lowest resistance. The forming of cavities could not be averted under all conditions.